1. Field of the Invention
The present invention relates to transparent electrodes useful in display devices.
2. Description of the Related Art
Flat panel display technology is becoming increasingly important in electronic devices requiring displays which range in size from wrist watches to lap-top computer screens to hang-on-the-wall TVs to scoreboards. These displays employ various technologies to create thin, high resolution displays wherein each pixel is activated by a set of electrodes. The electrodes activate the pixels by exciting voltage-responsive substances such as liquid crystals, plasmas, phosphors, and electroluminescent materials that are trapped between the electrodes. When the electrodes activate a pixel, light is transmitted to the viewer of the display. For many displays, one electrode must be made of a transparent material that does not interfere with the light reaching the viewer.
The transparent electrode material must be electrically conductive. Unfortunately, conductive materials which have transparent qualities also tend to have high electrical resistance when compared to opaque metallic conductors. The high resistance values may cause the display device to run at a slower rate, remove the voltage across the pixel variably and/or consume more power. Moreover, when the surface resistance of the transparent electrode drops below approximately 10 ohms per square, the electrodes have difficulty activating pixels for some, particularly larger, display types.
One approach for enhancing the conductivity of transparent electrodes is the depositing of a thin strip of highly conductive opaque material in contact with the transparent electrode. This strip will be hereinafter referred to as the opaque conductor. The opaque conductor usually comprises metals such as gold, silver, aluminum, copper, chrome, and combinations thereof. Opaque conductors deposited on the transparent electrode are preferably thick enough to reduce the resistance of the transparent electrode by two to four orders of magnitude. The opaque conductor, however, is not wide enough to noticeably block the light from the flat panel display from reaching the viewer.
Previous attempts to bring opaque conducting strips in contact with transparent electrodes include forming the opaque strip directly on a glass substrate, and then overlaying the transparent electrode on top of the opaque conducting strip and the substrate (see Tohda et al, U.S. Pat. No. 4,814,668, the contents of which are hereby incorporated by reference).
Another approach has been to form a strip of transparent electrode material directly on a glass substrate, and then deposit a strip of the opaque conductor that has one edge partially extended over the top of the transparent electrode strip, and the opposite edge over the side of electrode and making contact with the substrate (see Narniki et al, U.S. Pat. No. 5,399,936, the contents of which are hereby incorporated by reference).
A still further approach to contacting opaque conductors with transparent electrodes involves forming a strip of transparent electrode on a glass substrate and then sandwiching two opaque conducting strips on opposite sides of the electrode strip and also in contact with the substrate (see Cathey, U.S. Pat. No. 5,342,477, the contents of which are hereby incorporated by reference).
Unfortunately, it has proven difficult to provide an opaque conductor which properly adheres to the surface of the transparent electrode. Delamination of the opaque conductor from the underlying transparent electrode is a major problem in the development of transparent electrodes for display devices.